A circular plasmid of 3600 bp is cut with one enzyme…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A circular plasmid of bp is cut with one enzyme. The gel shows a band at bp, a band at bp and a band at bp that is twice as bright as the others.
- What do the three band sizes add up to?
- How much DNA is missing from the sum?
- What does the bright band tell you, and how many sites does the enzyme have?
Need a reminder? The key ideaShow
Read a size from a ladder with a straight line of size against distance. An uncut plasmid shows a supercoiled band (fastest), a linear band and a nicked band (slowest). The control plates are: no DNA, uncut vector, cut vector without ligase, and cut vector with ligase and no insert. Efficiency colonies (ng of DNA on the plate) for each microgram.
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Given. Plasmid bp. Bands , and bp, the last one twice as bright.
Plan. The fragments of a digest must add up to the plasmid.
Step 1. (a) bp.
Step 2. (b) bp are missing.
Step 3. (c) The missing bp is a second fragment of bp, which runs together with the first one in a brighter band. So there are four fragments: , , and bp. A circle with four fragments has sites.
Answer: bp; bp; two equal fragments in the bright band, and four sites.
Check. bp.
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